The present invention is concerned with a method to produce magnetically stable iron powder from an iron oxide or iron oxide hydrate. In particular, it is concerned with such a process in which the reduction rate is enhanced so that the reduction is achieved more quickly at a given temperature than is normally possible.
An object of the present invention is to produce an iron powder for magnetic recording which has high coercivity for improved short wavelength response, good orientability and high magnetic moment for high output and good chemical stability for safe handling and long storage. A further object of this invention is to provide a process to prepare said iron powder that is economically attractive. The magnetic material of this invention will find utility in the fields of magnetic copying, for example high speed printing, data storage (discs and tapes) and magnetic recording in the forms of audio and video tapes.
In the past, numerous schemes have been devised for producing iron powders for magnetic recording purposes. U.S. Pat. No. 3,607,220, calls for the treatment of iron powder with stannous chloride solution and then reduction and stabilization to form an iron powder. U.S. Pat. No. 3,623,859, uses bismuth to prevent sintering when making acicular iron particles from iron oxide. U.S. Pat. No. 3,627,509, uses silver to shorten the reduction time when making iron powder from iron oxide. U.S. Pat. No. 3,663,318, discloses a process to make iron powder from salts of iron, cobalt, nickel, and chromium using amineborane and tetrahydroborate. U.S. Pat. No. 3,740,266, discloses a mixture of iron oxide and iron alloys with cobalt or nickel which may contain from about 0.01 to 10% antimony. U.S. Pat. No. 3,837,839, discloses doping iron oxide hydrate with a metal which is catalytic for hydrogen (cobalt, nickel and ruthenium) to speed up the reduction rate. Both U.S. Pat. Nos. 4,063,000 and 4,069,073, list antimony as one of many other metals which may be added to improve unnamed properties of the powder. Finally, Dutch Pat. No. 134087, discloses the preparation of metallic particles by electrolytic precipitation in a liquid mercury cathode. Antimony, in an amount of 2-20 percent, is added to the mercury bath containing the metallic particles to prevent the metallic particles from sintering during the vacuum distillation of the mercury.